1. Field of the Invention
This disclosure relates to systems, processors, devices, and methods for measuring chemical constituents in tissue for diagnosing medical conditions. More specifically, it relates to systems, pulse sequences, signal and diagnostic processors, diagnostic displays, and related methods using novel application of nuclear magnetic resonance, including magnetic resonance spectroscopy, for diagnosing pain such as low back pain associated with degenerative disc disease.
2. Description of the Related Art
While significant effort has been directed toward improving treatments for discogenic back pain, relatively little has been done to improve the diagnosis of painful discs.
Magnetic resonance imaging (MRI) is the primary standard of diagnostic care for back pain. An estimated ten million MRIs are done each year for spine, which is the single largest category of all MRIs at an estimated 26% of all MRIs performed. MRI in the context of back pain is sensitive to changes in disc and endplate hydration and structural morphology, and often yields clinically relevant diagnoses such as in setting of spondlyolesthesis and disc herniations with nerve root impingement (e.g. sciatica). In particular context of axial back pain, MRI is principally useful for indicating degree of disc degeneration. However, degree disc degeneration has not been well correlated to pain. In one regard, people free of back pain often have disc degeneration profiles similar to those of people with chronic, severe axial back pain. In general, not all degenerative discs are painful, and not all painful discs are degenerative. Accordingly, the structural information provided by standard MRI exams of the lumbar spine is not generally useful for differentiating between painful and non-painful degenerative discs in the region as related to chronic, severe back pain.
Accordingly, a second line diagnostic exam called “provocative discography” (PD) is often performed after MRI exams in order to localize painful discs. This approach uses a needle injection of pressurized dye in awake patients in order to intentionally provoke pain. The patient's subjective reporting of pain level experienced during the injection, on increasing scale of 0-10, and concordancy to usual sensation of pain, is the primary diagnostic data used to determine diagnosis as a “positive discogram”—indicating painful disc—versus a “negative discogram” for a disc indicating it is not a source of the patient's chronic, severe back pain. This has significant limitations including invasiveness, pain, risks of disc damage, subjectivity, lack of standardization of technique. PD has been particularly challenged for high “false+” rates alleged in various studies, although recent developments in the technique and studies related thereto have alleged improved specificity of above 90%. (Wolfer et al., SPINE 2008) However, the significant patient morbidity of the needle-based invasive procedure is non-trivial, as the procedure itself causes severe pain and further compromises time from work. Furthermore, in another recent study PD was shown to cause significant adverse effects to long term disc health, including significantly accelerating disc degeneration and herniation rates (on the lateral side of needle puncture). (Carragee et al., SPINE 2009). Controversies around PD remain, and in many regards are only growing, despite the on-going prevalence of the invasive, painful, subjective, harmful approach as the secondary standard of care following MRI. PD is performed an estimated 400,000 times annually world-wide, at an estimated total economic cost that exceeds $750 Million Dollars annually. The need for a non-invasive, painless, objective, non-significant risk, more efficient and cost-effective test to locate painful intervertebral discs of chronic, severe low back pain patients is urgent and growing.
A non-invasive radiographic technique to accurately differentiate between discs that are painful and non-painful may offer significant guidance in directing treatments and developing an evidence-based approach to the care of patients with lumbar degenerative disc disease (DDD).
Previously reported lab experiments used 11 T HR-MAS Spectroscopy to compare chemical signatures of different types of ex vivo disc nuclei removed at surgery. (Keshari et al., SPINE 2008) These studies demonstrated that certain chemicals in disc nuclei, e.g. lactic acid (LA) and proteoglycan (PG), may provide spectroscopically quantifiable metabolic markers for discogenic back pain. This is consistent with other studies that suggest DDD pain is associated with poor disc nutrition, anaerobic metabolism, lactic acid production (e.g. rising acidity), extracellular matrix degradation (e.g. reducing proteoglycan), and increased enervation in the painful disc nuclei. In many clinical contexts, ischemia and lowered pH cause pain, likely by provoking acid-sensing ion channels in nociceptor sensory neurons.
The previous disclosures evaluating surgically removed disc samples ex vivo with magnetic resonance spectroscopy (MRS) in a laboratory setting is quite encouraging for providing useful diagnostic tool based on MRS. However, an urgent need remains for a reliable system and approach for acquiring MRS signatures of the chemical composition of the intervertebral discs in vivo in a readily adoptable clinical environment, and to provide a useful, clinically relevant diagnostic tool based on these acquired MRS signatures for accurately diagnosing discogenic back pain. A significant need would be met by replacing PD with an alternative that, even if diagnostically equivalent, overcomes one or more of the significant shortcomings of the PD procedure by being non-invasive, objective, pain-free, risk-free, and/or more cost-effective.